From Waste To Watts: How This Grocery Chain Turns Old Food Into New Energy03:57

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The anaerobic digester at Stop & Shop's distribution warehouse in Freetown reduces its energy costs and means the company creates less trash that it then needs to pay to haul away. (Courtesy Stop & Shop)

Each year billions of pounds of food go to waste.

That means billions of dollars, too. The Environmental Protection Agency says more food reaches landfills and incinerators than any other one material in our trash.

And for supermarkets, that leftover food equates to lost dollars. But now, one New England supermarket chain is trying to get some of those dollars back by sending old food once consigned to trash compactors to a giant energy plant in Massachusetts.

It's called an "anaerobic digester." It's basically a big metal stomach, which gobbles up old food — and turns that waste into power.

Turning Old Onion Rings Into Energy

I'm on the floor of Stop & Shop's distribution warehouse in Freetown, Mass. looking down a long line of garage doors. Each day, trucks unload old and expired food from over 200 New England stores — and, eventually, that organic waste turns into electricity.

Roger Beliveau, manager of distribution services for Stop & Shop, says a lot of that old food comes from produce departments.

"But within this facility, we can take it from any department — we can take packaged goods. So what you're looking at here is already-packaged onion rings, which are in a plastic container, which will go into the plant," he explains.

The story of how those onion rings get converted into electricity begins with an array of machines, which crank away as we talk. I watch as plastic packaging is separated from old food like wilted greens, expired dairy and even flowers. Then, all the organics get mixed down with water.

"It's turned into a slurry, basically a big slushie," says Kevin Stetson, an employee of Divert, the company Stop & Shop uses to run the food-to-energy plant.

Stetson says that "slushie" is slurped up by machines and fed at a steady rate into the core of the waste-to-energy plant: its anaerobic digester.

"The anaerobic digestion likes a steady state, just like humans," says Stetson. "We don't want to eat a big meal and then not eat for two days. We want to eat at a regular rate."

That balance is important. Because inside the anaerobic digester are bacteria, which gobble up that yummy milkshake and, eventually, release methane. The process is contained — so it doesn't smell — and that methane "biogas" is used to power a generator that, today, is spitting out about one megawatt of power.

That's not a lot, but at full bore, the unit outputs enough electricity to fulfill about 40 percent of the power needs for the more-than-1-million-square-foot distribution center.

Divert says right now, about 70 to 80 tons of food waste come in each day. And in the summer, that number is even higher. It's a lot of food. Or, looked at another way, a lot of lost money.

"When you waste less food as a company, you save money," says Dana Gunders, a senior scientist with the Natural Resources Defense Council and author of a 2012 paper examining wasted food in the U.S.

Nationwide, she says, grocers are taking a much closer look at the food they throw away.

"But generally speaking, if there's an empty shelf out there, that's viewed as a missed sale," Gunders says. "They want to make sure there's enough product on the shelf that when a consumer gets there and wants that product, that they can have it."

Gunders says the calculus of "acceptable losses" has changed in recent years. And, while it's still hard to find a misshapen carrot or bruised apple on a store shelf, grocers are taking a harder look at reducing waste — and costs — up and down their supply chains.

Back at the Stop & Shop plant, Beliveau says getting old food out of incinerators and landfills is good for the environment, sure, but the anaerobic digester is also good for his company's bottom line.

Bacteria inside the anaerobic digester feed on wasted food once its sorted. The digester then creates methane gas that can be used to generate electricity. (Courtesy Stop & Shop)

The digester reduces the cost of energy for a distribution center that runs 24/7 — and it means less trash that the company needs to pay to get rid of.

"Some of our stores are down to where they're maybe hauling their compactor once every other month versus, it could have been every two to three weeks," he says.

The digester makes a lot of compost, too -- every week about three dump-truck-loads of nutrient-rich soil, which, eventually, could help grow the next generation of produce lining supermarket shelves.